1. Field of the Invention
This invention relates to novel liquid crystalline compounds and liquid crystalline mixtures containing the same, and more particularly, it relates to chiral smectic compounds which have a high response rate and are superior as a ferroelectric liquid crystalline material, and also to chiral smectic mixtures containing the same.
2. Description of the Prior Art
Twisted nematic (TN) type display mode has currently been most widely employed as liquid crystal display elements, but it is inferior in response rate as compared with emissive type display elements such as electroluminescence, plasma display, etc., and various attempts for overcoming this drawback have been made. Nevertheless, it seems that its improvement to a large extent has not been fulfilled. Thus, various liquid crystal display equipments based on different principles in place of TN type display elements have been attempted, and as one of them, there is a display mode utilizing ferroelectric liquid crystals (N. A. Clark and S. T. Layerwall, Applied Phys. lett., 36,899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to SC* phase) or chiral smectic H phase (hereinafter abbreviated to SH* phase) of ferroelectric liquid crystals and those are preferred which exhibit these smectic phases at temperatures in the vicinity of room temperature. The present inventors have made various searches for liquid crystal substances containing an optically active group, mainly in order to develop liquid crystal substances suitable for being used for the above display mode, and as a result have attained the present invention.